1. Field of the Invention
The present invention relates to the general concept that electrically non-conductive materials, such as polymers, can be made conductive by adding a conductive material. More specifically, the present invention relates to understanding the influence that the shape, size, diameter, aspect ratio, branching and three dimensional interconnectivity of the additive conductive material has on overall material properties. Moreover, the importance of the preservation of the aspect ratio, branching, and interconnectivity in the final mixture is discussed.
2. Background
The process of adding conductive particles to a non-conductive medium, such as a polymer, to obtain a more conductive result is well known. Historically, the conductive additives are typically of the form of a sphere, plate, flake, rod, fiber, nanofibers, nanotubes, and so forth. These additive particles can vary in basic conductivity (such as ranging from carbon to nickel to copper to silver), size (from tens of millimeters to tens of nanometers), shape (such as plates, rods, or spheres, each format having its own associated packing factor), and most importantly, aspect ratio (the ratio of length to diameter). The essential concept in adding these conductive particles is to use them to increase the conductivity of the overall mixture of the non-conductor substrate that they are combined with, and also to alter the conductive nature of the substrate itself.
The following metals are exemplary of what is typically used by the current state of the art for conductive particles. Silver (Ag) is very highly conductive, but is also expensive, susceptible to corrosion, and has a high density. Copper (Cu) is highly conductive and has found widespread use in many applications, but is also susceptible to corrosion. Nickel (Ni) is a bit less conductive and moderately priced, with the added benefits of magnetism and corrosion resistance. Carbon (C) is not as conductive, but is also relatively inexpensive. Carbon nanofibers and nanotubes are very expensive; and while they individually are very conductive, they are not as conductive as anticipated when added to a polymer. This is because they are very difficult to evenly disperse and create a conductive network.
Combinations of these metals are sometimes used to find the right combination of required properties.